Tell a subway clerk you gotta get to the airport and he might let you in or else a cop would and then you’d be set. But in Britain, clerks hide behind the rules — “There’s nothing I can do,” rather than, “Let me see what I can do.”
One good thing about British bureaucracy, though, is that it’s inefficient and often leaves things undone. These are the holes you can wriggle through.
Such a hole was before me when I got to the tube station. An exit gate was wide open and nobody seemed to be watching it.